| 1. |
- Andrieux, Sebastien, et al.
(author)
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Monodisperse highly ordered chitosan/cellulose nanocomposite foams
- 2019
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In: Composites. Part A, Applied science and manufacturing. - : ELSEVIER SCI LTD. - 1359-835X .- 1878-5840. ; 125
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Journal article (peer-reviewed)abstract
- In solid foams, most physical properties are determined by the pore size and shape distributions and the organisation of the pores. For this reason, it is important to control the structure of porous materials. We recently tackled this issue with the help of microfluidic-aided foam templating, which allowed us to generate mono-disperse and highly ordered chitosan foams. However, the properties of foams also depend on the properties of the pore wall constituents. In case of chitosan-based foams, the foams have poor absolute mechanical properties, simply due to the fact that the solubility of chitosan in water is very low, so that the relative density of the freeze-dried foams becomes very small. Drawing inspiration from the field of nanocomposites, we incorporated cellulose nanofibres into the foamed chitosan solutions, with a view to strengthening the pore walls in the foam and thus the mechanical properties of the final foam. We report here how the cellulose nanofibres affect the structure of both the liquid foam template and the solid foam. The resulting nanocomposite foams have improved mechanical properties, which, however, are not proportional to the amount of cellulose nanofibres in the composites. One reason for this observation is the disturbance of the porous structure of the solid foams by the cellulose nanofibres.
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| 2. |
- Claesson, Per M., et al.
(author)
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Bottle-brush polymers : Adsorption at surfaces and interactions with surfactants
- 2010
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In: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 155:1-2, s. 50-57
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Journal article (peer-reviewed)abstract
- Solution and adsorption properties of both charged and uncharged bottle-brush polymers have been investigated. The solution conformation and interactions in solution have been investigated by small-angle scattering techniques. The association of the bottle-brush polymers with anionic surfactants has also been studied. Surfactant binding isotherm measurements, NMR, surface tension measurements, as well as SAXS, SANS and light scattering techniques were utilized for understanding the association behaviour in bulk solutions. The adsorption of the bottle-brush polymers onto oppositely charged surfaces has been explored using a battery of techniques, including reflectometry, ellipsometry, quartz crystal microbalance, and neutron reflectivity. The combination of these techniques allowed determination of adsorbed mass, layer thickness, water content, and structural changes occurring during layer formation. The adsorption onto mica was found to be very different to that on silica, and an explanation for this was sought by employing a lattice mean-field theory. The model was able to reproduce a number of salient experimental features characterizing the adsorption of the bottle-brush polymers over a wide range of compositions, spanning from uncharged bottle-brushes to linear polyelectrolytes. This allowed us to shed light on the importance of electrostatic surface properties and non-electrostatic surface-polymer affinity for the adsorption. The interactions between bottle-brush polymers and anionic surfactants in adsorbed layers have also been elucidated using ellipsometry, neutron reflectivity and surface force measurements.
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| 3. |
- Claesson, Per M., et al.
(author)
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Short-range interactions between non-ionic surfactant layers
- 2006
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 8:47, s. 5501-5514
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Research review (peer-reviewed)abstract
- Short-range interactions between surfactant and lipid layers are of great importance in technical applications in complex fluids such as foams, dispersions and emulsions, as well as in the formulation and performance of dispersants, detergents and flocculants. It is also of utmost importance in biological systems where interactions between biomembranes influence a range of processes. The field of short-range interactions has been thoroughly investigated during the past 30 years, following the emergence of a number of techniques to measure interaction forces, Thus, our understanding has increased considerably and it is timely to summarize relevant knowledge accumulated in this area. In this review we focus on the nature of short-range interactions between non-ionic and zwitterionic surfactant and lipid layers exposing their polar groups to the surrounding medium. We discuss the complex interplay of short-range (van der Waals, hydration, steric and other) forces based on recent theoretical and experimental results.
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| 4. |
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| 5. |
- Fameau, Anne Laure, et al.
(author)
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Liquid foams as sensors for the detection of biomarkers
- 2023
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In: Journal of Colloid and Interface Science. - 1095-7103 .- 0021-9797. ; 651, s. 987-991
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Journal article (peer-reviewed)abstract
- Bioassays are widely used in healthcare to detect and quantify biomarkers, such as molecules or enzymes, which are crucial in monitoring diseases and health conditions. In developed countries, healthcare professionals use specialized reagents and equipment's to perform these bioassays. However, in less-industrialized countries, the creation of low cost, fast, and technically simple bioassays is required. Herein, we propose a simple approach for detecting biochemical markers using host–guest complexes containing a surfactant. When the biochemical marker is present, the host–guest complex is disrupted, releasing the surfactant and producing foam. The read-out mechanism relies on the change of foam volume as function of biomarker concentration. This change is quantifiable by the naked eye and can be measured with a simple ruler. We claim that the use of foams as sensing tool is an attractive, inexpensive, fast, and easy to handle on-site detection method.
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| 6. |
- Gilanyi, Tibor, et al.
(author)
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Adsorption of alkyl trimethylammonium bromides at the air/water interface
- 2008
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 317:2, s. 395-401
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Journal article (peer-reviewed)abstract
- A number of features of the adsorption of alkyl trimethylammonium bromides with n(c) = 10, 12, 14, and 16 at the air/water interface were studied. First, the adsorption isotherms were calculated front experimental surface tension vs concentration curves by means of the Gibbs equation. Second, a novel method was used to estimate the adsorption free energy change. From the analysis of these data it was concluded that the hydrophobic driving force for the adsorption first increases with increasing adsorbed amount and then levels off in a plateau, which holds true for all four homologues. This peculiar behavior was interpreted by the formation of a thin liquid-like alkane film at the air/water interface once a certain adsorbed amount is exceeded. The hydrophobic contribution to the standard free energy change of adsorption was compared with those values previously determined for alkyl sulfate homologues. This comparison suggests that the alkyl trimethylammonium type surfactants behave as if their alkyl chain was approximately one methylene group shorter than those of the corresponding alkyl sulfates.
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| 7. |
- Laupheimer, Michaela, et al.
(author)
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Transmission Measurements as Tool to Study Phase Transitions of Liquid Mixtures
- 2014
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In: Tenside Surfactants Detergents. - : Walter de Gruyter GmbH. - 0932-3414 .- 2195-8564. ; 51:1, s. 17-25
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Journal article (peer-reviewed)abstract
- We present a quantitative method to determine the phase transition temperatures between one-phase and two-phase regions of multi-component liquid mixtures via temperature-dependent transmission measurements with an UV/Vis spectrometer. The method is based on the fact that multi-phase samples are turbid, while one-phase samples are transparent. We describe the method in detail and discuss the choice of the experimental parameters (wavelength, sample layer thickness), a suitable temperature program as well as the data analysis. We prove the validity of our method by measuring the phase diagrams of two model systems, namely a liquid and a gelled nnicroemulsion. The results are in good agreement with those obtained with the conventional visual method used for phase studies.
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| 8. |
- Preisig, Natalie, et al.
(author)
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How Promoting and Breaking Intersurfactant H-Bonds Impact Foam Stability
- 2019
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In: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 35:47, s. 14999-15008
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Journal article (peer-reviewed)abstract
- On the basis of previous results revealing that intersurfactant H-bonds improve foam stability, we now focus on how foams stabilized by two different N-acyl amino acid surfactants are affected by different salts (NaF, NaCl, NaSCN), which can promote or break intersurfactant H-bonds. The chosen surfactants, namely, sodium N-lauroyl sarcosinate (C12SarcNa) and sodium N-lauroyl glycinate (C12GlyNa), differ only by one methyl group at the nitrogen of the amide bond that blocks intersurfactant H-bonds in the case of C12SarcNa. The salts were chosen because they are kosmotropic (NaF), chaotropic (NaSCN), and in between (NaCl) and thus influence the formation of an H-bond network in different ways. Surface tension measurements showed that the addition of salts decreased the cmcs of both surfactants and increased the packing density, as expected. Moreover, in presence of the salts, the head groups of the H-bond forming surfactant C12GlyNa were more tightly packed at the surface than the C12SarcNa head groups. The effect of the salts on foam stability was studied by analysis of the foam height, the foam liquid fraction, and by image analysis of the foam structure. As expected, the salts had no significant effect on foams stabilized by C12SarcNa, which is unable to form intersurfactant H-bonds. In contrast, the stability of C12GlyNa-containing foams followed the trend NaF > NaCl > NaSCN, which is in agreement with NaF promoting and NaSCN breaking intersurfactant H-bonds. Surface rheology measurements allowed us to correlate foam stability with surface elasticity. This study provides new insights into the importance of H-bond promoters and breakers, which should be used in the future design of tailor-made surfactants.
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| 9. |
- Ranieri, Davide, et al.
(author)
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On the Influence of Intersurfactant H-Bonds on Foam Stability : A Study with Technical Grade Surfactants
- 2018
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In: Tenside Surfactants Detergents. - : CARL HANSER VERLAG. - 0932-3414 .- 2195-8564. ; 55:1, s. 6-16
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Journal article (peer-reviewed)abstract
- From the literature on the foam stability of various surfactants with C-12 alkyl chains but different head groups a clear picture emerges: Foams are more stable when hydrogen bonds can form between the head groups, i.e. when the polar head group has a hydrogen bond donor and a proton acceptor. These observations suggest that hydrogen bonds between neighbouring molecules at the surface enhance foam stability. To support this hypothesis, we carried out a systematic foaming study of two types of technical grade surfactants, one of them being capable of forming H-bonds and the other one not. As was the case for the pure surfactants we found again that more stable foams are formed when the head group is capable of forming intersurfactant H-bonds: These results will certainly affect the future design of surfactants.
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| 10. |
- Rippner Blomqvist, Brita
(author)
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Non-ionic block copolymers and proteins at the air-water interface
- 2005
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Doctoral thesis (other academic/artistic)abstract
- The behavior of block copolymer and protein films at interfaces is of central importance to their function in many application areas. Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers function e.g. as emulsifiers and in coatings in oral, parenteral, and topical pharmaceutical formulations and are also widely used for cleaning purposes. The globular protein β-lactoglobulin is the most abundant whey protein and it is used within the food industry as a component of many common foods. To understand the interfacial behavior of block copolymers and proteins in such applications one has to study molecular processes like adsorption, the responses to shear and dilatational deformation of the interface (i.e. surface rheology), conformational changes of the molecules, and forces that are generated between interfacial layers. Such investigations form the focus of the work presented in this thesis. Thin film measurements with a series of block copolymers composed of poly(ethylene oxide) and poly(butylene oxide) revealed that the thickness of foam films (air-aqueous solution-air) is determined by electrostatic and steric repulsion. The range of the steric repulsion is directly dependent on the size of the polymer, in particular the length of the poly(ethylene oxide) chains. Block copolymers attached to the air-water interface change their conformation with increasing surface concentration. The study of the dilatational modulus as a function of the surface pressure of spread and adsorbed block copolymer layers showed that the block copolymers pass from a two-dimensional conformation to a three-dimensional extended structure as the available area per molecule decreases. Relaxation processes occur mainly by a redistribution of segments within the surface layer. Mixing of the hydrophobic poly(propylene oxide) segments in a sublayer of poly(ethylene oxide) and water was proposed to occur at high surface concentration of the polymer. Conformational changes (partial denaturation) of globular proteins upon adsorption at the air-water interface leads to the formation of highly viscoelastic networks, which play an important role for the stabilization of foams and emulsions. Mixed layers, formed by competitive adsorption of β-lactoglobulin and block copolymers, were also investigated. On increasing the concentration of block copolymer, the viscoelasticity of the mixed protein/block copolymer layer gradually decreased. The polymer was able to displace the protein from the interface. The drainage rate of thin liquid films was also enhanced by the presence of block copolymer. Whether or not the incorporation of the polymer in the β-lactoglobulin layer has a detrimental effect on foam stability depends on the ability of the polymer to generate long-range steric repulsion across the foam films. For pure block copolymer systems, correlations between foam stability and the thickness of interfacial layers, in the steric regime, were found. The results obtained can be utilized for increasing the understanding of the mechanisms for foam stabilization in both model and industrial systems.
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